Tracking energy consumption using a sepic-converter technique

ABSTRACT

The invention relates to an apparatus and method for tracking energy consumption. An energy tracking system comprises at least one switching element, at least one inductor and a control block to keep the output voltage at a pre-selected level. The switching elements are configured to apply the source of energy to the inductors. The control block compares the output voltage of the energy tracking system to a reference value and controls the switching of the switched elements in order to transfer energy for the primary voltage into a secondary voltage at the output of the energy tracking system. The electronic device further comprises an ON-time and OFF-time generator and an accumulator wherein the control block is coupled to receive a signal from the ON-time and OFF-time generator and generates switching signals for the at least one switching element in the form of ON-time pulses with a constant width ON-time.

FIELD OF THE INVENTION

The invention relates to an electronic device and a method for trackingthe energy consumption, and more specifically to an electronic deviceand a method for determining energy consumption using the principle ofstoring energy in an inductor and transferring the energy into outputenergy storing components.

The present application relates to jointly owned U.S. Patent Applicationcorresponding to application Ser. No. 13/329,073 entitled, “ElectronicDevice and Method for Power Measurement.”

BACKGROUND

Reducing energy consumption is important in the development andimprovement of electronic devices, in particular if they are mobile orportable electronic devices. In order to save energy, electronic devicesare more and more controlled by sophisticated schemes in which themagnitude of the consumed currents varies over several decades ofmagnitude. In low power modes some hundreds of nA (nano-amperes) of acurrent may be consumed while other operation modes require up toseveral hundreds of mA (milli-amperes). It is often necessary to measurethese currents over a wide range (e.g. from nano-amperes tomilli-amperes) with an acceptable accuracy while at the same time beingable to track highly dynamic current changes. Furthermore, any sideeffects due to measuring the consumed energy should be avoided or wellcontrolled. For example, it is preferred that an increase of the energyconsumption due to the energy measurement itself not occur.

One of the more common techniques for measuring a current is ameasurement using a shunt device or a shunt resister. Using a shuntdevice for the power measurement requires very high precision analogueto digital converters in order to cover the full dynamic range of thepossible magnitudes of the currents. For example, when four and a halfdecades of measurement with one percent precision is required, a24-Bit-converter would be required. Furthermore, shunt devices generatea voltage drop. This voltage should be compensated, while thecompensation circuitry constitutes a potential source of errors. Directload compensation can be difficult. This means that the measurementrange and therefore the circuitry used for measuring the powerconsumption has to be adapted during the energy measurement procedure.This increases complexity and entails more potential errors.

Still further, measuring a current indirectly by measuring the voltageacross a shunt device requires an initial voltage change on the target.If a buffer capacitor is coupled to the target side (output side of anenergy transfer circuits), the buffer capacitor delivers currentimmediately and needs to be recharged. This behavior affects the truecurrent response of the device under test. Another approach of measuringthe energy consumption employs a current mirror. One side of the currentmirror delivers the current to the target including the targetcapacitor. The other side of the current mirror is coupled to an Amperemeter to which the mirrored current is fed. This approach has theadvantage that the distortion caused by the target capacitor isminimized. However, the required pairing of the power and sense fieldeffect transistors (FET) is rather poor and is not capable of trackingthe huge current magnitude to be supported.

SUMMARY

It is an object of the invention to provide an electronic device 200 anda method for measuring energy consumption in an energy consuming systemthat covers a large range of magnitudes of supply currents, high dynamiccurrent changes and does not affect the basic functionality of thecircuit which energy consumption is measured. According to an aspect ofthe invention, an electronic device 200 is provided that comprisesswitched mode energy tracking circuitry. The switched mode circuitrycomprises one or more switching elements SW1 a-SWia and SW1 b-SWib, oneor more in inductors, IND1 a and INDia and a compare circuit 406 thatcontrols the output voltage level VO at a selected voltage level. Theswitching elements, SW1 a and SW1 ia, are configured to switch currentthrough the inductors IND1 a and INDia respectively. The switches, SW1a-SWib and SW1 ia-SW1 ib, may be transistors. The voltage comparecircuit 406 may be an error amplifier, a voltage comparator, or an A/Dconverter which conversion result is compared to a reference voltageVL(ref). The ON/OFF generator 408 is configured to control the ON-timeand OFF-time of the switching elements, SW1 a-SW1 ia and SW1 b-SW1 ib,in order to transfer energy from a primary energy source, e.g. powersupply, to the output VO of the energy tracking system and to controlthe level of the output voltage VO. The electronic device 200 furthercomprises control logic stages CNTL1-CTNLi. A control block 410comprises an error handling block 420, reporting block 416, acalibration block 428, an accumulator 430 of the individual ON-timeevents, a sequencing block 422, a range control block 418 and a demandcontrol block 424.

The control logic stages CTNL1-CNTLi generate the switching signals SWS1a to SWSib for the switched transistors, SW1 a-SW1 ia and SW1 b-SW1 ib,in the form of ON-time pulses with a constant width ON-time. The controllogic stages, CTNL1-CNTLi, also control the OFF-time which is used alsoas an indicator of the energy in the inductors that is transferred tothe output VO. The voltage-compare circuit 406 flags when the nextON-time pulse has to be generated. If the OFF-time is not over beforethe next ON-time is triggered, the system reports an error condition. Anerror condition is also reported if the output voltage VL is not withinpredefined limits.

The switching signals, SWS1 a to SWSib, are formed according to a pulsedensity scheme. The highest density of pulses occurs when the On-timeand OFF-time are met at the time another ON-time is requested. Higherdensity is enabled by default or by control information (e.g. a controlbit and this is handled by the control circuit as described previously).In an embodiment of the invention, the pulse accumulator 430 can be inthe simplest implementation a digital counter. The counter in thisembodiment is then configured to count the number of ON-time pulses fordetermining the consumed power based on the number of ON-time pulses pertime. The constant pulse width of the ON-time pulses makes the influenceof the system components such as the non-linear behavior of switchedtransistors or inductors negligible. The target voltage offset at theoutput of the energy tracking system is highly reduced. A wide range ofmagnitudes of the measured current can be covered.

According to another aspect of the invention, the electronic device 200comprises a first capacitor C1 coupled to the input of the energytracking system and a second capacitor C2 coupled to the output of theenergy tracking system. The ON-time of the switching element inconjunction with the inductor's value IND1 and the value of thecapacitor C1 is configured to keep the voltage within the systemaccuracy requirements. The output capacitor C2 is of such value that thevoltage increase during transferring the energy from the inductor IND1 ato INDia is within the accuracy expectations.

The energy tracking system of this embodiment is contrary to a pulsewidth modulation scheme and nearly all energy in the inductors, IND1a-INDib can be transferred to capacitor C2. The frequency of the ON-timepulses is proportional to and practically a linear function of theconsumed current. During a settled operation condition, in which theinput and output voltages and the charges on the input and outputcapacitors have settled, each ON-time pulse of the switched transfersabout the same amount of the energy.

According to another embodiment of the invention, a reference impedance205 or a reference resistor R can be coupled to the output of the energytracking system in order to make a reference energy measurement. Theresults of the reference measurement(s) can then be used for calibratingthe system to the energy consumption. Therefore, the number of theON-time pulses can be used for determining the energy consumption duringnormal operation even with an unknown load (e.g. C3 & Z). The unknownload according to an embodiment of the invention can be an electronicdevice.

In an embodiment of the invention, the electronic device 200 comprisesan energy tracking system with switching components SW1 a-SW1 ia and SW1b-SW1 ib, inductors IND1 a-INDib, capacitors Ck and Ci and a transfersupport diodes D1-Di. The switching components SW1 a-SW1 ia and SW1b-SW1 ib can then be configured to enable current through the inductorsIND1 a-INDib. The voltage compare circuit 406 can be an error comparatoror error amplifier. The voltage compare circuit 406 is configured tosend a signal 426 to the control circuit 410 and the ON/OFF generator408 so that the switching components SW1 a-SW1 ia and SW1 b-SW1 ib canbe triggered or be prepared to be triggered. The error handling circuit420 serves to deliver the demand on energy to maintain a stable outputvoltage VO. The generation and frequency of the ON-time pulses can becontrolled in response to a change of the output voltage VL. The ON-timepulses can be combined with a time stamp on an individual basis or on agroup of pulses.

Another embodiment of the invention includes ON-time pulses that arebased on a defined time and the difference to that defined time base isbounded by pulses or a group of pulses. The energy consumption may thenbe determined based on the number of the ON-time pulses per consideredtime period.

In an aspect of the invention, the energy consumption may then bederived from a phase variation of the ON-time pulses. This aspect allowsa quick evaluation of changes of the power consumption. The energytransfer during ON-time pulses usually is significantly smaller than theenergy stored on a first capacitor C1 coupled to the input of the energytransfer system. The energy withdrawn from the energy source at theinput of the energy transfer system influences the energy transferredduring the ON-time. The influence of the energy sourcing capability is afactor in the calibration cycle.

The energy stored on a second capacitor C2 coupled to the output of theenergy transfer system is also significantly larger than the energystored in the inductor during the ON-time and transferred to the outputand the capacitor C2 during OFF-time. The energy consumption may becalibrated by coupling one or more reference impedances 205 to theoutput of the energy transfer system. The result of the calibration maythen be used for normalizing the energy consumption during normaloperation. During normal operation a target device or a device undertest (DUT) 208 is then coupled to the output of the energy transfersystem instead of the reference impedance 205. However, in anotherembodiment, the reference impedance 205 may be coupled to the outputwhile the target load device or DUT 208 is still coupled to the output.The energy of one or a group of ON-time pulses due to the additionalload of the reference load can be evaluated for calibrating the powermeasurement based on the energy pulse ON-time and OFF-time conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a circuit measuring the current, the voltage and the timingrelations to calculate the energy consumed within the load of thedevice-under-test. (Prior Art)

FIG. 2 is a simplified circuit diagram of an embodiment of theinvention.

FIG. 3 is a diagram showing waveforms of signals of the circuit shown inFIG. 2 according to an embodiment of the invention.

FIG. 4 is a circuit diagram of an embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows a circuit 101 that measures the load current via avoltage-to-voltage converter 102, an A/D converter 104 and timer 106.The energy EL used by the load is calculated in block EL 108. Thevoltage VL is measured via the A/D converter 104. When the A/D converter104 is used for sequential conversions, phase related errors may occur.A timer 106 is used to create the time base t(b) for the A/D converter104. The energy EL used by the load (i.e. DUT) is calculated by theblock EL according to equation 1 below.

EL=IL*VL*t(b)   Equation 1

FIG. 2 shows a simplified diagram of an embodiment of the invention. Inthis embodiment, an energy tracking system 200 comprises energy transferblocks 202 and 204, a control circuit 201 and reference impedance 205.In this embodiment, each energy transfer block 202 and 204 comprises twoswitched transistors, a capacitor, a diode and two inductors. Forexample, energy transfer block 202 comprises switched transistors SW1 aand SW1 b, diode D1, capacitor Ck and inductors IND1 a and IND1 b. Inthis example two energy transfer blocks 202 and 204 are shown. However,more than two energy transfer blocks may be used. A first inductor in anenergy transfer block is coupled with one side to a first switchedtransistor and a capacitor and with the other side of the first inductorto an input of the energy transfer block. The switched transistors canbe referred to as energizing switches. The diodes may be replaced orcomplemented by a second switch. The control circuit 201 controls theenergy switches SW1 a, SW1 b, SW1 ia and SW1 ib. The control circuit 201will be explained in more detail later in the specification.

FIG. 3 shows the timing diagram for an energy transfer circuit that hastwo transfer paths. The first path has SW1 a, IND1 a, Ck, D1, and theON-time signal SWS1 a applied to SW1 a. The second switch SW1 b shown inenergy transfer block 202, in this example, is not used. The second pathhas SW1 ia, INDia, Ci, Di, and the ON-time signal SWSia applied to SW1ia. The second switch SW1 ib shown in energy transfer block 204, in thisexample, is not used. The two energy transfer paths are used mainly toenhance the dynamic range of delivering energy. The signals SWS1 b andSWSib for switches SW1 b and SW1 ib respectively are optionally used toreduce the energy losses through diodes D1 and Di respectively. Thesystem may have more than 2 paths enabling further spread of the dynamicrange.

FIG. 4 shows more detail in the control circuit 201. The compare circuit406 is coupled to receive an reference signal VL(ref) that is used todetermine a deviation of the output voltage VL. The output signal 426 ofthe compare circuit 406 is coupled to the control logic stages CNTL1 402and CNTLi 404, the error handling block 420 and the ON/OFF generator408. The ON/OFF generator 408 is coupled to feed the ON-time signals TG1and TGi to the control logic CNTL1 and CNTLi respectively. The controllogic stage CNTL1 provides switching signals SWS1 a with constant widthON-time pulses for switching the switching element SW1 a. The controllogic stage CNTL1 provides optionally the signal SWS1 b to cause theswitch SW1 b to conduct during the transfer of energy from the inductorIND1 to the output V0/C2. The control logic stage CNTLi providesswitching signals SWS1 ia with constant width ON-time pulses forswitching the switching element SW1 ia. The control logic stage CNTLiprovides optionally the signal SWSib to cause the switch SWib to conductduring the transfer of energy from the inductor INDi to the outputV0/C2.

Issuing the next ON-time pulses is a function of the output signal 426of the compare circuit 406 and the ON/OFF-time. The constant widthON-time is generated in this embodiment from a constant clock (e.g. froma crystal oscillator). Such an implementation eases the calibrationsituation since the ON-time is nearly independent of the voltage andtemperature conditions. The primary side of the energy tracking systemis coupled to a first capacitor Cl. Accordingly, one side of theinductor IND1 a is coupled to one side of the first capacitor C1. Theother side of the first capacitor C1 is coupled to ground. The primaryside of the energy tracking system is supplied by a stable power supply206. The output or secondary side of the energy tracking system iscoupled to a second capacitor C2 for buffering the output voltage VO. Atarget board or device under test 208 can be coupled to the output ofthe energy tracking system. The current consumed by the target board ordevice under test is the load current IL The level of the output voltageis VO.

One or more reference impedances 205 in the form of reference resistor Rand a switch LS can be coupled through switch LS to the energy trackingsystem. Instead of the target board the reference resistor R can beswitched to the output VO. However, the target board or DUT 208 maystill be coupled to the output VO during the reference measurement. Theresult of the reference measurement with the well characterizedreference resistor R can then be used to calibrate the measurement forthe operation with the unknown load (e.g. C3 & Z) of the target board208. The energy transferred through the switched transistors SW1 a, SW1ia during an ON-time pulse is usually much smaller than the energystored on the capacitors C1 and C2. If the energy that is transferredduring an ON-time pulse is ESW, and the energy on capacitor C1 is EC1,and the energy on capacitor C2 is EC2, the following advantageous ratiosare:

EC1=k1*ESW

and

EC2=k2*ESW

with

k1 and k2>50.

ESW is much smaller than EC2 and EC1. When the output voltage VO hassettled, the compare block measures any deviation of target outputvoltage VL versus VL(ref). The control blocks CNTL1 and CNTLi increaseor decrease the density of ON-time pulses. The ON-time pulses aregenerated with a constant width ON-time and a minimum OFF-time. Theinductors IND1 and INDi will be charged with a certain amount of energyfrom the first capacitor C1. During the OFF-time the energy ESW1 andESWi in the inductors IND1 a and INDia is transferred to the secondcapacitor C2. In an embodiment of the invention, the first capacitor C1and the second capacitor C2 are sized such that this energy transferdoes not significantly change the voltages across the first capacitor C1and the second capacitor C2.

As long as the energy in the second capacitor C2 is sufficient tomaintain the output voltage VO, the compare block will not requestanother ON-time pulse through switching signals SWS1 a, SWS1 b or SWSia,SWSib. However, if a certain load current IL is consumed by the targetboard or DUT, the voltage across the second capacitor C2 is reduceduntil the voltage compare block VL=VL(ref) determines that the outputvoltage VO at output node OUT is lower than defined and generates arequest signal to CNTL1 and CNTLi. Another ON-time pulse will then begenerated. During normal operation, this causes a pulse density ofON-time pulses of signals SWS1 a and SWSia that is proportional to theconsumed energy of the DUT/target board 208. In another embodiment, thenumber of ON-time pulses per time counted by the accumulator and thecurrent data there reflects and indicates the energy consumption. Understable input voltage conditions, each ON-time pulse represents thesubstantially the same amount of energy that is transferred during eachON-time pulse. The OFF-time variations of the ON-time pulses of theswitching signals SWS1 a and SWS1 ia also indicate current variations ofthe load currents IL.

A reference measurement on the known reference resistor R can be usedfor normalizing the measured current. The reference resistors R may beswitched on through switch LS in addition to the target board 208. Theinfluence of the reference resistor R on the pulse density of theON-time in signals SWS1 a and SWS1 ia can then be evaluated. However,the achieved result can be improved if the reference resistors R areswitched on while the target board is not connected.

FIG. 3 shows a diagram with waveforms of the load current IL, the outputvoltage VO, and ON-time signals as applied to switches SW1 a and SW1 ia.The load current IL of the target or DUT increases at a certain point oftime. The voltage VO at the output node OUT varies according to a sawtooth scheme around the target output voltage level. The pulse densityof the ON-time pulses SWS1 a and SWSia increases at a certain point oftime or starts (SWSia) depending on the extent of the load current IL.The voltage VO varies according to a saw tooth scheme around the targetoutput voltage level (dashed line). The pulse density of the ON-timepulses increases after the load current IL increases. This change indensity of ON-time pulses of both paths is evaluated.

Although the invention has been described hereinabove with reference toa specific embodiments, it is not limited to these embodiment and nodoubt further alternatives will occur to the skilled person that liewithin the scope of the invention as claimed.

1. An electronic device comprising an energy tracking system, the energytracking system comprising at least one energy transfer block and acontrol circuit wherein the control circuit is configured to controlswitching of energy in the at least one energy transfer block in orderto transfer energy from a primary voltage applied at an input of theenergy tracking system into a secondary voltage at the output of theenergy tracking system; wherein the control circuit comprises an ON-timeand OFF-time generator, at least one control logic block and anaccumulator wherein the at least one control logic block is coupled toreceive a signal from the ON-time and OFF-time generator and to generateswitching signals for the at least one energy transfer block in the formof ON-time pulses with a constant width ON-time, and wherein theaccumulator is configured to collect the number of ON-time pulses fordetermining the consumed energy based on the number of ON-time pulsesper time; wherein the at least one energy transfer block comprises: afirst inductor having a first terminal and a second terminal wherein thefirst terminal is connected to an input of the at least one energytransfer block; a first switching element, the first switching elementbeing connected to the control circuit, to ground and to the secondterminal of the inductor; a first capacitor having a first terminal anda second terminal wherein the first terminal of the first capacitor isconnected to the second terminal of the first inductor; and a secondinductor having a first terminal and a second terminal wherein the firstterminal of the second inductor is connected to the second terminal ofthe first capacitor and the second terminal of the second inductor isconnected to ground.
 2. The electronic device of claim 1 wherein the atleast one transfer block further comprises: a diode having a cathode andan anode wherein the anode is connected to the second terminal of thecapacitor and the cathode is connected to an output of the at least oneenergy transfer block; a second switching element, the second switchingelement being connected to the control circuit, the second terminal ofthe capacitor and to the cathode of the diode.